/// <summary>
 /// 取消收藏
 /// </summary>
 /// <param name="sender"></param>
 /// <param name="e"></param>
 private void menuRemove_Click(object sender, RoutedEventArgs e)
 {
     if (selected_item != null)
     {
         _viewModel.ExchangeFavorite((selected_item as Story).ID);
     }
 }